This invention relates to display systems and more particularly to the generation of characters or lines on a display device with high accuracy without the use of expensive precision electronic components.
In the prior art, the generating of lines on a cursive display is accomplished by defining successive points along a line with a precision digital-to-analog (D/A) converter followed by a delay line integrator in each axis. A precision 13-bit D/A converter operating at high conversion rates of approximately 3 MHz translates the successive point definitions into successive level definitions containing transitional "glitches". A special de-glitching circuit removes virtually all these glitches and provides its output to a tapped delay line integrator. The integrator breaks each major step into a series of smaller steps thereby raising the roughness frequency components to approximate 30 MHz. A low frequency filter is used to remove the high frequency roughness and produces the desired smooth voltage waveform. However, the high quality D/A's and de-glitcher used in this approach are relatively expensive components.
Another approach in the prior art uses less precise D/A's whereby one D/A is used to define a starting position anywhere on a display screen and another D/A is used to feed an analog integrator to produce the desired line relative to that starting position. These two waveforms are summed together to form the final output to X or Y deflection amplifiers. Again in such an open loop-system, expensive precision components are generally employed to minimize line drift due to component aging or temperature effects. Even then, the interaction between positions defined by a reference position D/A and positions defined by a D/A integrator results in a high frequency of maintenance adjustment and a performance compromise of display position-line registration.